1. Field of the Invention
The present invention relates to a drive device, and specifically relates to a drive device using an electromechanical conversion element or transducer such as a piezoelectric element, for example, a drive device suitable for precision driving of a probe of a tunnel scanning type electron microscope, a camera photographic lens, or an XY drive table.
2. Description of the Related Art
Conventionally, a drive device using an electromechanical transducer has been proposed. The applicants have previously proposed a drive device capable of high resolution in the order of the submicron level using a piezoelectric linear actuator in place of a stepping motor.
An example of such drive device using an electromechanical transducer is shown in FIG. 1A. The drive device 1 of FIG. 1A provides a drive unit 20 friction bonded in space 9 between a pair of fixed friction members 4 and 6 fixedly attached to the top surface 2s of base 2. One fixed friction member 6 is supported on base 2 via a holding spring 8, which exerts a force toward the other fixed friction member 4.
Specifically, drive unit 20 comprises a moving body 24 having a relatively large mass connected to a driven member, for example, a lens, stage or the like not shown in the drawing, a piezoelectric element 22, and a friction drive member 26 having a relatively small mass. One endface of piezoelectric element 22 in the direction of expansion/contraction is fixedly attached to moving body 24, and the other endface is fixedly attached to one axial endface of friction drive member 26. Friction drive member 26 is supported on moving body 24 so as to be freely movable in the direction of expansion/contraction of piezoelectric element 22.
More specifically, piezoelectric element 22 is one type of electromechanical conversion element, comprising a plurality of layered piezoelectric panels which change volume when a voltage is applied, so as to expand and contract in the layer direction via changes in the applied voltage. Moving body 24 is largely columnar in shape, and has screw holes 24a and 24b for mounting driven members not shown in the drawing. The top surface of moving body 24 is notched downward so as to form two concavities 24s and 24t, which accommodate piezoelectric element 22 and friction drive member 26, respectively. Friction drive member 26 is provided with extending shafts 26t at bilateral ends of a cylindrical main body 26s, each shaft 26t being supported by moving body 24 so as to be freely movable in the axial direction, and one shaft 26t being fixedly connected to piezoelectric element 22. The main body 26s of friction drive member 26 has a larger width than does either piezoelectric element 22 or moving body 24, such that the exterior surface of main body 26s is in contact with the surfaces 4s and 6s of the pair of opposed fixed friction members 4 and 6, respectively.
Each electrode of piezoelectric element 22 is connected to a drive pulse generating circuit not shown in the drawing, which supplies to piezoelectric element 22 a pulse voltage of suitable waveform such as a sawtooth shape, full rectified wave and the like. For example, the speeds of the expansion and contraction of piezoelectric element 22 may differ so as to generate sliding of different magnitude in the reverse direction between friction drive member 26 and fixed friction members 4 and 6, or sliding may be generated in only one direction with either the expansion or contraction of piezoelectric element 22 with no sliding with the other action so as to move friction drive member 26 and in conjunction therewith the moving body 24 and driven members along the fixed friction members 4 and 6.
In drive device 1, when there is a relative change in position of the drive unit 20 relative to the fixed friction members 4 and 6, the magnitude of the pressing force received by friction drive member 26 from the fixed friction members 4 and 6 changes in conjunction with the change in inclination and elastic deformation of the fixed friction member 6, thereby changing the frictional force between the friction drive member 26 and fixed friction members 4 and 6 so as to change the drive conditions. As a result, the drive speed and drive force change in accordance with the relative positions of the friction drive member 26 and the fixed friction members 4 and 6.